Recently, most computers and communications apparatus use large-scale integration (LSI) circuits each having large numbers of transistors and resistors integrated into a single chip with interconnections. Thus, the performance of the entire apparatus depends greatly on the performance of the LSI chip. The performance of the LSI chip can be upgraded by increasing the packing density, that is, scaling down the dimensions of on-chip devices.
Scaling down the dimensions of devices can be achieved by optimizing the ion implantation and subsequent thermal annealing in forming diffusions such as source/drain diffusions. This allows MOS devices with shallow source/drain diffusions of 0.2 xcexcm or less in depth to be realized.
In order to form such shallow diffusions, it is required to make a low thermal budget so that impurity atoms are distributed shallow upon ion implanting and are not diffused deep in the subsequent thermal process.
On the other hand, in order to form through impurity doping a well in which a device, such as a MOS transistor, is formed and a region (a channel doped layer) in which the channel of the MOS transistor is induced, it is required to control precisely the implant dose.
The production of MOS transistors having channels of opposite conductivity type or MOS transistors having different threshold voltages in the same substrate inevitably requires the use of a resist mask in each of ion implantation processes for wells, channels, or polysilicon gate electrodes.
That is, it is required to coat a layer of resist onto the entire surface, remove portions of the resist that are located above regions where ion implantation should take place to thereby define a resist pattern, and ion-implant impurities into the regions using this resist pattern as a mask.
This approach involves a sequence of steps of resist coating, exposure to light, resist development (resist pattern formation), ion implantation, resist ashing, and wet cleaning using H2SO4xe2x80x94H2O2 mixture.
The ion implantation (ion irradiation) has been extensively used as a method of forming pn junctions by introducing impurities, such as boron (B), phosphorus (P), arsenic (As), etc., into a semiconductor substrate. This ion implantation method allows impurities to be introduced into target sites with their concentration and depth controlled precisely.
The ion source chambers at the heart of ion implantation apparatus are roughly classified into three: the Burnus type, the Freeman type, and the microwave type that uses a magnetron.
FIGS. 16A and 16B show, in sectional view, the conventional Burnus type ion source chamber. More specifically, FIG. 16A is a sectional view taken parallel to the top of the ion source chamber, and FIG. 16B is a sectional view taken parallel to the side of the chamber. On one side of an arc chamber 71 is mounted a tungsten filament 77 by insulating supports 75 and reflectors (spacers). On the opposite side is mounted an electrode 74 by an insulating support 75 so as to be opposed to the filament 77.
Next, description is given of a method of extracting ions using this apparatus. A gas, such as an Ar gas, is introduced into the arc chamber through a gas inlet 72 and thermal electrons are released from the tungsten filament 77. The direction of movement of the thermal electrons is changed to the reverse direction to the direction of emission from the filament by the opposed electrode 74, thereby increasing the probability of collision of the thermal electrons with the Ar gas introduced into the arc chamber to ionize the Ar gas. The resulting ions are taken out of the chamber through an ion outlet 23 provided in a front plate 78.
FIGS. 17A and 17B show, in sectional view, the conventional Freeman type ion source chamber. More specifically, FIG. 17A is a sectional view taken parallel to the top of the chamber, and FIG. 17B is a sectional view taken parallel to the side of the chamber. On the opposed sides of an arc chamber 91 are mounted reflectors 96 by insulating supports 95. A bar-like tungsten filament 99 is attached to the opposed reflectors 96.
Next, description is given of a method of taking out ions using this apparatus. A gas, such as an Ar gas, is introduced into the arc chamber through a gas inlet 92 and thermal electrons are released from the tungsten filament 97. At the same time, a magnetic field parallel to the filament 97 is produced by electromagnets 100 and a rotating magnetic field is produced by a current in the filament electrode. Within the arc chamber 91 the movement of electrons is disturbed by the action of the reflectors 96, thereby increasing the probability of collision of thermal electrons emitted by the tungsten filament 97 with the Ar gas introduced into the arc chamber. The resulting ions are taken out of the chamber through an ion outlet 93 provided in a front plate 98.
FIG. 18 shows, in sectional view, of the microwave type ion source chamber. To take out ions using this apparatus, microwaves are generated by a magnetron 111 and then introduced into a discharge box 113 through a waveguide 112, thereby generating a plasma in the discharge box, which corresponds to the above-described arc chamber. The resulting ions are taken out through an electrode 114.
In these conventional ion source chambers, ions to be implanted are generally obtained by introducing a gas or vapor produced by sublimating a solid into the arc chamber and ionizing the gas or vapor by the aforementioned plasma. That is, in the conventional ion source chambers, ions are required to be supplied in the form of vapor or gas. However, with a refractory metal such as boron or titan, in order to obtain a vapor pressure of the order of 1E-4TORR necessary for ion implantation, it is required to heat the metal to a very high temperature (for example, 1400xc2x0 C. or above for titan). In practice, ion implantation is impossible with this method.
Conversely, indium, having a melting point as low as 156xc2x0 C., melts easily in plasma and hence is very inconvenient to use.
On the other hand, an ion implantation method has been developed which uses gases of chlorides or fluorides of those metals, enabling those low melting point metals to be used. However, this method inevitably causes corrosion of the inner walls of the arc chamber and the thermal electrons emitting filament due to chlorine, fluorine, chloride compounds, or fluoride compounds resulting from chloride gases or fluoride gases.
For indium as well, an attempt was made to use its chloride gas. For example, when vapor obtained by heating InCl3 to 330xc2x0 C. is introduced into the conventional ion source chamber shown in FIGS. 16A and 16B for the purpose of ion implantation, chlorine ions or radicals dissociated from InCl3 etch not only the inner walls of the arc chamber that is made mainly of tungsten but even the tungsten filament. As a result, the filament becomes thinned considerably, resulting in an increase in resistance and failure to perform necessary control for arc discharge. In addition, even the outlet electrode is etched, disabling ions from being taken out stably. As a result, a large number of abnormal discharges comes to occur in about five hours, disabling ion implantation.
Thus, so long as chlorine-based compounds are used to ionize the refractory metals and indium, etching reaction due to chlorine ions or chlorine radicals resulting from the ionization inevitably occurs in the inner walls of the arc chamber and the tungsten filament.
Moreover, when a chloride gas, such as indium chlorine, and a fluoride gas, such as boron fluoride or germanium fluoride, are alternately introduced into the same arc chamber and then ionized, fluorine is attracted to the walls at the time when the boron fluoride is introduced and then reacts with chlorine at the time when the chloride gas is introduced to form chlorine fluoride that is a strong oxidizing agent. This accelerates the corrosion of the inner walls of the arch chamber and the thermal electron emitting filament although they are made of aluminum, stainless or stable refractory metals such as tungsten, molybdenum, and graphite. Furthermore, it becomes necessary to remove bad effect of fluorine and chlorine in exhaust gas, increasing the apparatus cost.
In the case of an oxide gas, on the other hand, carbon (graphite)-based members used in an ion generator or ion irradiation apparatus, particularly electrodes for taking out ions, are oxidized, which significantly reduces the life of the apparatus.
In particular, the filament suffers corrosion due to chlorine and fluorine, thus making it difficult to obtain stable arc discharge over a long period of time. With noble metals, such as gold and platinum, that are difficult to obtain their chlorides, ion implantation is still very difficult.
Further, a solid fluoride has deliquescence and, while being loaded into a heating oven, reacts with moisture in atmosphere to dissolve. It is thus very inconvenient to use.
To solve the problems described so far, the inventors of this invention disclosed in Japanese Unexamined Patent Publication No. 10-188833 a method which, as illustrated in FIGS. 19A to 19C as an improved version of the Burnus type ion source chamber, places a plate-like material 79 consisting of a desired ion source within the arc chamber 71, generates a plasma in the arc chamber, and subjects the material to sputtering to generate desired ions (hereinafter referred to as sputtered ions). This method is excellent in that, unlike the previously described methods, ions of refractory metals can be generated with ease. In FIGS. 19A to 19C, like reference numerals are used to denote corresponding parts to those in FIGS. 16A and 16B.
Even with this method using sputtered ions, however, it is still very difficult to implant stably ions of a metal, such as indium, which is low in melting point and a metal, such as antimony, whose solid is unstable.
In ion implanting p-type impurities and n-type impurities using conventional semiconductor substrate manufacturing methods, it is a common practice to use separate ion or exchange source gases or solid sources serving as ion sources. In the former case, two or more ion implantation apparatuses are needed for processing of the same semiconductor substrate. In the latter case, a time is required to confirm conditions for stable ion implantation after an exchange is made. Either of these cases becomes a problem in reducing the semiconductor device manufacturing cost.
Ion implantation apparatus of the present invention comprises an electrically conductive mask having an opening and located apart from an object to be processed; and an ion implanting section which implants ions into the object through the opening of the electrically conductive mask.
Here, the conductivity of the conductive mask means not only conductivity such as metals have but conductivity in the range between metals and insulators such as semiconductors have.
With such ion implantation apparatus, desired regions of an object to be processed can be selectively implanted with ions through the conductive mask having openings formed. Thus, for different ion implantation processes, a separate conductive mask can be used for each of the ion implantation process, eliminating the need of using any resist pattern.
Therefore, the prior need of a sequence of processes of resist coating, exposure to light, resist development, ion implantation, resist ashing, and wet cleaning using H2SO4xe2x80x94H2O2 mixture can be eliminated, simplifying the ion implantation processes. As a result, the time and cost required to manufacture LSI devices can be reduced. Furthermore, heat treatment can be performed to reduce lattice defects in each ion-implanted layer in number, without the necessity of conducting a ashing process to remove the resist. The ion implanted layers can therefore have a lower defect density. This helps to greatly enhance the performance and reliability of the LSI element.
An ion generator of the present invention comprises a container formed in a shape of a box; a holding section which holds a solid material that includes a plurality of elements on an inner wall of the container; a plasma generating section which generates a plasma in the container to thereby sputtering the solid material held by the holding section in the container for generating ions of the plurality of elements; a gas introducing section which introduces into the container a plasma-generating gas for generating a plasma used for sputtering the solid material; a liquid trapping section which traps a liquid resulting from the sputtering; and a taking out section which takes plural species of ions generated by sputtering the solid material out of the container.
An ion implantation apparatus of the present invention comprises a container formed in a shape of a box; a holding section which holds a solid material that includes a plurality of elements on the inner wall of the container; a plasma generating section which generates a plasma in the container to thereby sputtering the solid material held by the holding section for generating ions of the plurality of elements; a gas introducing section which introduces into the container a gas for generating a plasma used for sputtering the solid material; a liquid trapping section which traps a liquid resulting from the sputtering; a taking out section which takes a plural species of ions generated by sputtering the solid material out of the container; and a directing section which directs a selected desired species ion of the plural species of ions taken out of the container by the taking out section onto an object to be processed.
Such an ion generator or ion implantation apparatus allows liquid of an ion generating element resulting from sputtering to be trapped in the liquid trap. Thereby, the liquid can be prevented from being exposed to the plasma. Thus, as ion generating elements, low-melting point elements or unstable elements can be used without the occurrence of abnormal discharges. Stable ion implantation can be performed.
Still another ion implantation apparatus of the present invention comprises a container formed in a shape of a box; a holding section which holds a solid material that includes a plurality of elements on a inner wall of the container; a plasma generating section which generates a plasma in the container to thereby sputtering the solid material held by the holding section for generating ions of the plurality of elements; a gas introducing section which introduces into the container a gas for generating a plasma used for sputtering the solid material; a liquid trapping section which traps a liquid resulting from the sputtering; a taking out section which takes a plural species of ions generated by sputtering the solid material out of the container; a directing section which directs a selected desired species ion of the plural species of ions taken out of the container by the taking out section onto an object to be processed; and an electrically conductive mask located apart from the object to be processed and having openings formed to allow the selected desired species ion of the plural species of ions to pass through.
Such an ion implantation apparatus can provides the advantages of the two ion implantation apparatuses described above.
A semiconductor device manufacturing method of the present invention comprises the steps of introducing a gas into a container in which a solid material including a plurality of elements is held; converting the gas into a plasma in the container, irradiating the solid material with the plasma to thereby sputtering the solid material and generating ions of the plurality of elements; trapping a plurality of elements in liquid form generated on the surface of the solid material during the step of generating the ions of the plurality of elements in a liquid trap; taking the plural species of ions generated by the sputtering the solid material out of the container; directing the plural species of ions taken out of the container toward an objected to be processed; and irradiating a desired object to be processed with the directed plural species of ions.
Another semiconductor device manufacturing method of the present invention comprises the steps of introducing an inert gas and a nitrogen gas into a container in which a material including a plurality of elements is held; converting the inert gas and the nitrogen gas into plasmas in the container, irradiating the solid material with the plasmas of the inert gas and the nitrogen gas to thereby sputtering the solid material and generating ions of the plurality of elements; nitriding a liquid including an element of the plurality of elements generated on the surface of the solid material during the step of generating the plurality of ions with the nitrogen gas; taking the plural species of ions generated by the sputtering the solid material out of the container; directing the plural species of ions taken out of the container toward an objected to be processed; and irradiating a desired object to be processed with the directed plural species of ions.
According to such semiconductor manufacturing methods, two or more ion species can be generated by sputtering the material. That is, ions required can be generated without exchanging ion sources. Thereby, p-type impurities and n-type impurities can be implanted successively without exchanging ion sources. Thus, the cost required to manufacture semiconductor devices can be reduced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.